Focus in Java,Java Focus Event,Java Focus Listener,How to Write Focus Listener in Java

Handling Focus Changes in Java

Introduction

In this section, you will learn about handling the focus changes in java. This section shows you how the event be handled according to the focuses and to find out whether the component got the focus or lost the focus.

This program determines the focus changes events. You can set the different-different events for the focused of the several components particularly. The generated focus events are performed by the FocusListener of the object used in your application using the addFocusListener() method. The generated event (FocusEvent) is passed to every FocusListener objects that receives such types of events using the addFocusListener() method of the object. The addFocusListener() method is takes the instance of MyFcousListener class.

MyFocusListener:
This is the inner class used in the FocusChange class in which, the focusGained() method has been used to receive the generated event. This method sets the text of the source of the event to the label component. This program displays the three command buttons on the frame. If you select any button of those then the text of that button will be shown on the label.

FocusAdapter:
This is the abstract class is used to receive the keyboard focus event.

Here is the code of program:


import java.awt.*;

import java.awt.event.*;



public class FocusChange{

  Label label;

  public static void main(String[] args){

    FocusChange fc = new FocusChange();

  }



  public FocusChange(){

    Frame frame = new Frame("RoseIndia.Net");

    Panel panel = new Panel();

    Button yes = new Button("Yes");

    Button no = new Button("No");

    Button cancel = new Button("Cancel");

    yes.addFocusListener(new MyFocusListener());

    no.addFocusListener(new MyFocusListener());

    cancel.addFocusListener(new MyFocusListener());

    panel.add(yes);

    panel.add(no);

    panel.add(cancel);

    frame.add(panel,BorderLayout.NORTH);

    label = new Label();

    frame.add(label,BorderLayout.CENTER);

    frame.setSize(400,400);

    frame.setVisible(true);

    frame.addWindowListener(new WindowAdapter(){

      public void windowClosing(WindowEvent we){

        System.exit(0);

      }

    });

  }



  public class MyFocusListener extends FocusAdapter{

    public void focusGained(FocusEvent fe){

      Button bt = (Button)fe.getSource();

      String str = bt.getLabel();

      label.setText(str);

    }

  }

}